This invention relates to disc drive spindle assemblies, and more particularly, to a disc drive spindle assembly which can be fabricated easily and assembled without the use of adhesives.
In a co-pending U.S. patent application Ser. No. 08/286,287 filed Aug. 5, 1994 for Adhesiveless Disc Drive Spindle Assembly, by Macleod et. al (hereinafter Macleod application), assigned to Seagate Technology, discloses a novel overmolded stator assembly, the teachings of which are fully incorporated herein by reference. FIG. 1 shows a plan view of a disc drive base and a stator assembly showing the stator clamping arrangement of the Macleod disclosure which is reproduced here. FIG. 2 shows an enlarged cross sectional view of the stator clamping mechanism of the Macleod disclosure. FIG. 3 shows an enlarged cross sectional view of the stator clamping mechanism during tension of the clamp string, per Macleod disclosure while FIG. 4 shows an alternate clamp spring arrangement.
Now referring to FIG. 1, Magnet 78 is preferably polarized into eight separate polarization sectors, each sector occupying about 45.degree. and having opposite polarity as adjacent sectors. Stator assembly 80 preferably includes twelve radially positioned electromagnets 82. Electromagnets 82 include core 84 made of six sheets of laminated iron and wrapped with coil 86 of wire. Any exposed surface of core 84 is sealed with coating 98 to reduce corrosion. Plastic bobbin 88 is shown and is helpful in winding coils 86 about cores 84. Current is provided to coil 86 through flexible printed circuit (not shown). While electromagnets 82 are usually spaced equidistant form each other and spaced as closely as possible to magnet 46 to provide a uniformly reversing magnetic field as strong as possible with the least possible current. FIG. 1 further shows electromagnets 82 encased in overmold 92. Overmold 92 is preferably a plastic material, a bulk molding compound of thermoset molding material based on unsaturated polyester resin and containing inorganic fillers such as calcium carbonate, aluminum trihydrate and chopped short glass fiber. Overmold 92 encloses coil 86 and securely holds the wires in place to prevent movement of coil wires during motor operation and apparently helping to eliminate acoustic noise.
As best shown in FIGS. 1-3, stator 80 is retained in stator bed 102 of base 100 by three fastener assemblies 104. Stator bed 102 is shaped to prevent radial movement of stator 80. Fastener assembly 104 includes clamp spring 106, clamp washer 108 and fastener 110, which attaches to flange surface 112 of base 100. Clamp spring 106 is preferably made of flat stainless steel, and during bending acts as a spring. Fastener 110 is preferably a screw threaded fastener to provide ease of upward and downward adjustment. As shown in FIGS. 2 and 3, flange surface 112 is slightly below clamping surface 96 of stator 80, providing an offset 114. Clamping surface 96 may be the surface of coating 98 (as shown), or another surface such as that of core 84, coil 86 or overmold 92. As depicted alternatively in FIGS. 1 and 6, fastener assembly 104 may be used either with or without use of an overmold on stator 80.
In the Macleod application, the operation of fastener assembly 104 is as follows. As shown in FIG. 2, clamp spring 106 originally has a planar surface which covers offset 114. As fastener 110 is tightened down (FIG. 3), head 110 of fastener 110 begins to bend clamp spring 106 due to offset 114. The clamping force provided by clamp spring 106 on stator surface 96 is dependent on the amount of bending of clamp spring 106. Clamp spring 106 is configured such that a designated amount of bending (e.g., preferably an amount between 10 and 30.degree., such that a slight gap 115 is left between head 110 and the far edge of clamp spring 106 after tightening) will provide a proper securing for stator 80 under load conditions. The function of clamp washer 108 is to prevent any damage to coating 98 or core 84 caused by clamp spring 106 as fastener 110 is tightened down. Accordingly, clamp washer 108 may be made from a soft cloth-like or elastic material, but is preferably plastic or MYLAR.
FIG. 4 shows a plan view of an alternative clamp spring band 118 for use in fastening stator 80 to base plate 100. Rather than using three separate clamp springs 106, this singular clamp spring band 118 has band 120 which extends approximately 270.degree. around stator 80 and holds together three clamp spring portions 122. The larger C-shaped clamp spring band 118 has three fastener locations 124 and thus can be used identically as three individual clamp springs 106 to clamp stator 80 in place.
The overmold stator assembly of Macleod disclosure uses a coating 98 on exposed surface of core 84 to avoid corrosion while plastic bobbin 88 is used to wind the coils 86 about cores 84 and route the wires of the coils 86 from one core to another. Once the coils 86 are wound, the electromagnets 82 are encased in overmold 92. Further, the fastener assembly of Macleod disclosure requires plurality of clamp springs 106, clamp washer 108 and a fastener 110. In addition, the current is provided to the coil 86 using a printed circuit. There is a need to reduce the number of parts required to assemble a stator assembly. There is a need to reduce the number of parts to fasten a stator assembly to the base. There is also a need to reduce the number of manufacturing steps required to assemble a stator assembly and fasten the stator assembly to the base. There is also a need to reduce the length or the presence of the flexible printed circuit so that any adverse electrical or magnetic effects of current flowing through the printed circuit to the coils can be reduced or eliminated.